D3 - Hello World
This example demonstrates the simplest possible D3 program: a single text element reading “Hello D3 version 7” rendered directly in the browser’s body. It shows how a D3 selection and the `select` function from the `d3` module target an existing HTML element and replace its content. The code uses the `d3.select` API to hook into the DOM, while the accompanying `index.html` provides an empty body as the target. No data is involved; the focus is purely on initializing D3 and verifying the library loads correctly.